Field
Various communication systems may benefit from techniques and systems for resource allocation. For example, communication systems of the third generation partnership project may benefit from device to device discovery resource allocation methods and systems.
Description of the Related Art
Third generation partnership project (3GPP) long term evolution advanced (LTE-A) release 12 or 13 (Rel-12/13) may include features related to device to device discovery and communications. Currently, proximity services (ProSe)/Device-to-Device (D2D) discovery and communication is one issue that is relevant to such standardization. D2D discovery is one of the D2D scenarios that can be considered.
In 3GPP D2D discovery, at least two types of resource allocation methods are thought to be possible: Type-1 & Type-2 resource allocation. For Type-1 resource allocation, D2D discovery devices, such as a user equipment (UE), conventionally share a common resource pool. Thus, a UE can autonomously select the resource to be used for discovery signal transmission. For Type-2 resource allocation, eNB can conventionally assign a UE-specific resource for discovery signal transmission. Idle mode UEs are supposed to be able to discover other UEs and be discovered by other UEs. Thus, supporting Type-1 resource allocation may be necessary in order for an idle mode UE to obtain resources without the need to enter into Radio Resource Control connected (RRC_connected) state for resource allocation, as with Type-2 resource allocation.
A D2D discovery signal can be sent on a cellular uplink (UL) subframe (SF). In this discussion, this subframe is referred to as a “D2D SF”. Moreover, cellular and D2D data may not be allowed to be multiplexed in a frequency division multiplexing (FDM) way from one UE perspective. According to such an approach, if a UE sends a discovery signal in a D2D SF, this UE cannot transmit on a physical uplink control channel (PUCCH) or on a physical uplink shared channel (PUSCH) simultaneously in the same SF, namely in the D2D SF.
If RRC_Connected mode UEs use type-1 resource allocation, a potential issue arises when cellular and D2D traffic co-exist and when a connected mode UE is very heavily scheduled in DL. For example, if one UE has DL data transmission on physical downlink shared channel (PDSCH) in every DL SF, this UE will conventionally consequently send acknowledgment/negative acknowledgment (ACK/NACK or A/N) on PUCCH on every UL SF. The resulting issue is that this UE will conventionally find no place to send discovery message.
Similarly, if UE is heavily scheduled on PUSCH, UE will conventionally have reduced possibilities for discovery signal transmission.
One way to address this issue is to set D2D discovery signal transmission with higher priority than cellular data or control. However, with Type-1 resource allocation, the eNB cannot conventionally predict in which UL SF UE will send D2D discovery signal. If D2D discovery signal were set with higher priority, eNB would have to assume that any PUCCH in D2D SF could be unavailable, which would affect cellular services, as there would be DL retransmissions of data for which UEs were not able to send A/N. Likewise, DL would also be affected because of UEs not being able to send channel quality information (CQI) in the normal way. If discovery signal transmissions would prevent utilizing a scheduled PUSCH resource, UL resources would be wasted.